Hundreds of well-off Japanese and other nationals are turning to China's burgeoning human organ transplant industry, paying tens of thousands of pounds for livers and kidneys, which in some cases have been harvested from executed prisoners and sold to hospitals.

When Kenichiro Hokamura's kidneys failed, he faced a choice: wait for a transplant or go online to check out rumours of organs for sale. As a native of Japan, where just 40 human organs for transplant have been donated since 1997, the businessman, 62, says it was no contest. "There are 100 people waiting in this prefecture alone. I would have died before getting a donor." Still, he was astonished by just how easy it was.

Ten days after contacting a Japanese broker in China two months ago, he was lying on an operating table in a Shanghai hospital receiving a new kidney. "It was so fast, I was scared," he says. The "e-donor" was an executed man; the price: 6.8m yen (about £33,000).

Beijing does not reveal how many people it executes, but analysts estimate as many as 8,000 people are killed each year. Reports of Chinese authorities removing organs from executed prisoners have been circulating since the mid-1980s, when the development of a drug called Cyclosoporine-A made transplants a newly viable option for patients.

Until now, most of the evidence linking executions to the organ trade has been anecdotal and has not been helped by a lack of transparency in the Chinese criminal justice system or the secrecy that surrounds prison executions.

A recovering Mr Hokamura claims he is concerned with where his new kidney came from. "My translator said my donor was a young executed prisoner," says the businessman. "The donor was able to provide a contribution to society so what's wrong with that?"

"It was cheap," adds Mr Hokamura, now back in Japan. "I can always earn more money."

Rumours of problems with follow-up care and patients dying within one to two years of returning from China have failed to stem the tide.

A single broker has helped more than a hundred Japanese people go to China for transplants since 2004 and the trade is growing. Official figures almost surely underestimate the numbers of people, many of whom fly without government knowledge. Mr Hokamura says his family is so pleased that his daughter has put his experience on the internet. In her blog she says she feels sorry for others to have to wait years for transplants and provides a link to a support centre in Shanghai. "Other people should know about this," she writes.

Sources say the cost of a kidney transplant runs to £37,000 and for a liver up to £88,000. Mr Hokamura paid another million yen for transport costs. There is little attempt to conceal the origins of the organs, the bulk of which are taken from executed prisoners.

Alarmed by the growing traffic, the Japanese health ministry has begun a joint research project with transport authorities in a bid to gain some control on the trade. But the government is likely to find it difficult to stop desperate people who have money from making the short plane hop to China. Says Mr Hokamura: "I was on dialysis for four years and four months. I was tired of waiting."

The Chinese government insists it is trying to crack down on the market in illegal organs. According to regulations, even in the case of a donation by a close living relative, both patients and donors must provide legal proof of the relationship by blood or marriage or submit to a DNA test.

But the signs spray-painted on the walls outside clinics and hospitals in many parts of China tell a different story. Simple and direct, these show a mobile phone number and the character for shen, which means "kidney", written alongside. Postings on numerous online bulletin boards and other internet sites also offer kidneys for sale.

The sale of organs for transplants is illegal in China, but the black market is flourishing. And it's not just the small private hospitals and clinics springing up all over the country - even bigger hospitals in the capital Beijing and the business hub of Shanghai have adverts in toilet cubicles and on the walls of wards.

"We have to wipe off the notices again and again. They even visit doctors, make numerous calls or write letters again and again," said Professor Ding Qiang, the head of Urology at Huashan hospital, part of Fudan university in Shanghai. "Donations that are subsequently made are surely organ trading, but 'organ donation' for money is strictly banned," said Professor Ding.

However, China is a huge country and, as the proverb goes: the mountains are high and the emperor is far away. The legal ban may have an impact on the illegal organ trade in major public hospitals but the private clinics and small hospitals, which are run for profit, are extremely difficult to regulate, leaving room for profitable, illegal organ trading.

Generally, there is a lack of awareness in China about transplants. As in Japan, a cultural taboo, strongly related to Buddhist beliefs, has traditionally been associated with donating organs. The procedure is seen to make the body imperfect and, in some ways, it means the donor is being unfilial, even if the donation is to a family member.